This application claims the priority of Korean Patent Application No. 10-2004-98878, filed on Nov. 29, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to organic electroluminescence display devices and methods of manufacturing the same, and more particularly to an organic electroluminescence display device configured to prevent a pixel shrinkage phenomenon caused by deterioration of an organic electroluminescent layer.
2. Description of the Related Technology
An organic electroluminescence display device, such as an organic light emitting diode (OLED) display, has desirable characteristics such as spontaneous emission, wide viewing angle, fast response, small thickness, low production cost, and high contrast. Therefore, much attention has been paid to the organic electroluminescence display device as a next generation flat display device.
An exemplary organic electroluminescence display device comprises an anode electrode, a cathode electrode, and an organic electroluminescent layer interposed therebetween. Electrons and holes supplied from the respective anode and cathode electrodes are combined into electron-hole pairs in an excited state thereof, wherein these excited electron-hole pairs can be referred to as excitons. When the excitons return to a ground state, the energy difference between the excited and ground states is emitted as visible light.
Organic electroluminescence display devices are classified into a passive matrix type and an active matrix type, according to their pixel driving schemes, and the devices are arrayed in an N×M matrix. In a passive matrix type organic electroluminescence display device, the anode and cathode electrodes are arranged perpendicular to each other, and the pixels are driven by line selection. In the active matrix type organic electroluminescence display device, a pixel electrode of each pixel, that is, a display region, is connected to a thin film transistor, and the voltage of the pixel is maintained by capacitance of a capacitor connected to the thin film transistor.
More specifically, in the active matrix type organic electroluminescence display device, each unit pixel includes a switching transistor, a driving transistor, a capacitor, and an electroluminescence (EL) element, such as a light emitting diode. A voltage supply line Vdd is provided as a common power source to the driving transistor and the capacitor. The voltage supply line Vdd controls the current through the driving transistor to the EL element. In addition, an auxiliary electrode line is provided as an auxiliary power source to a second electrode. The auxiliary electrode line provides a current by generating a potential difference between source/drain electrodes and the second electrode.
FIG. 1 is a cross sectional view of an exemplary active matrix type organic electroluminescence display device. Referring to FIG. 1, the conventional active matrix type organic electroluminescence display device 10 comprises a substrate 100 having panel and wire regions A and B, and a buffer layer 105. A semiconductor layer 110, comprising source/drain regions 110c and 110a and a channel region 110b, is disposed on the buffer layer 105 in the panel region A. In one embodiment, the source/drain regions 110c and 110a and the channel region 110b are formed by a patterning process.
The display device 10 further comprises a gate insulating layer 120 disposed over the semiconductor layer 110, and a gate electrode 130 corresponding to the channel region 110b formed on the gate insulating layer 120 in the panel region A. An interlayer insulating layer 140 is formed on the gate electrode 130 over substantially the entire surface of the substrate 100. Following formation of the interlayer insulating layer 140, source/drain electrodes 145 are connected to the source/drain regions 110c and 110a through contact holes 141 formed in the interlayer insulating layer 140 in the panel region A. The semiconductor layer 110, the gate electrode 130, and the source/drain electrodes 145 form a thin film transistor (TFT).
A first conductive pattern 147, comprising substantially the same material as that of the source/drain electrodes 145, is also formed in the wire region B. The first conductive pattern 147 forms the aforementioned auxiliary electrode line. Subsequently, an insulating layer 150, such as a passivation layer and a planarization layer, is formed on the source/drain electrodes 145 and the first conductive pattern 147, and over substantially the entire surface of the substrate 100. Next, the insulating layer 150 formed on the upper portion of the first conductive pattern 147 in the wire region B is removed by a lithography process, for example.
A via hole 155 is formed on the insulating layer 150 in the panel region A to expose one of the source/drain electrodes 145. A first electrode 170 is formed by a patterning process so as to contact the source/drain electrodes 145 through the via hole 155, and extend to the insulating layer 150.
Following formation of the first electrode 170, to the exclusion of the wire region B, a pixel defining layer 175 having an opening 178 is formed on the first electrode 170 and the insulating layer 150. Next, an organic layer 180, including at least an organic electroluminescent layer, is formed on the first electrode 170 exposed by the opening in the panel region A. The organic layer 180 may be formed, for example by a patterning process. A second electrode 190 is formed on the organic layer 180 over substantially the entire surface of the substrate 100. Thereby, the second electrode 190 in the wire region B is electrically connected to the first conductive pattern 147.
In some organic electroluminescence display devices, the first conductive pattern 147 comprises the same material as that of the source/drain electrodes 145 in the panel region A, and a line width of the first conductive pattern 147 may be large. The materials of the first conductive pattern 147, molybdenum (Mo), tungsten (W), and molybdenum tungsten (MoW), have a higher heat capacity than a silicon nitride (SiNx) layer of the insulating layer 150. The “heat capacity” of a substance is the amount of heat energy required to change its temperature by one degree, and has units of energy per degree. Because of the differences in heat capacity between the first conductive pattern 147 and the silicon nitride layer, the first conductive pattern 147 cannot effectively transfer heat to the silicon nitride layer. As a result, reflow is not effectively performed between each of the panel regions during the organic layer curing process. Thereby, the effects of the curing process are different between the panel regions of a display, causing the thicknesses of the organic layers to be different between the panel regions of the display. In addition, gases remaining in the organic layers may cause pixel shrinkage. Specifically, the out-gassing or gases remaining in an organic layer may result in deterioration of the organic electroluminescent layer of the display.
Furthermore, a small line width of the first conductive pattern 147 may cause IR drop at the second electrode. IR drop is a signal integrity effect caused by wire resistance and current drawn from power and ground grids. If wire resistance is too high or the cell current larger than predicted, an unacceptable voltage drop may occur. This results in poor performance and increased noise susceptibility.